JUN (c-Jun,p39) forms the AP-1 early response transcription factor together with c-Fos. Under normal conditions, JUN plays a vital role in cell cycle progression, growth regulation and protection from UV-induced apoptosis. It is also a proto-oncogene that is frequently deleted, amplified or deregulated in cancer and is implicated in tumorigenesis in the breast, lung, liver and elsewhere. Additionally, JUN is an injury signaling protein, and overexpression of JUN in cortical and DRG neurons in the brain has been shown to promote regeneration. In immunohistochemistry, JUN has nuclear positivity in neurons in the cerebral cortex and cerebellum in the brain, and is positive in fractions of cells in most other tissues. References: The EMBO Journal. 18 (1): 188–97, PMID: 9878062; Cancer Research. 56 (2): 305–15, PMID: 8542585; Nat Rev Neurosci. 2018 Jun;19(6):323-337, PMID: 29666508;